1. Field of the Invention
The present invention relates broadly to internal combustion engines and, more particularly, to an internal combustion engine having a variable ratio crankshaft assembly for varying a stroke of the internal combustion engine over all strokes of engine operation. The present invention is applicable to both two- and four-cycle engines.
2. Description of the Prior Art
Conventional fixed stroke internal combustion engines operate according to a predetermined cycle characterized by four consecutive phases: intake, compression, expansion, and exhaust. In such engines, pistons reciprocate between a top dead center (TDC) and a bottom dead center (BDC). A distance the piston travels during an excursion through the cylinder between TDC and BDC is called a stroke. A four-stroke cycle engine requires four piston strokes (or two full revolutions of a crankshaft) to complete one cycle. In contrast, a two-stroke cycle engine requires two piston strokes (or one full revolution of the crankshaft) to complete one cycle. xe2x80x9cCyclexe2x80x9d is used to describe the complete power cycle, such as Otto cycle. This usage is consistent within this art and, in context, should not confuse those skilled in the art.
The internal combustion engines having a variable ratio crankshaft assemblies (or variable stroke crankshaft assemblies) are well known in the prior art. This is achieved by means of an arrangement that varies the position of the piston relative to a head of the cylinder. Such an arrangement is used to modify the effective piston strokes, such as to increase the stroke during the expansion event to increase the torque output, and/or to reduce the piston stroke during the intake and exhaust portions of the cycle, in order to increase the efficiency of the internal combustion engine.
The present invention provides an improved internal combustion engine including at least one cylinder having a central axis and a variable ration crankshaft assembly employed to extend a dwell point of a piston and improve connecting rod leverage. The crankshaft assembly comprises a gear set having a gear ratio 1:1 and including a first gear member non-rotatably mounted to an engine block and meshing a second gear member drivingly coupled to an eccentric member rotatably mounted between to a crankpin of the crankshaft assembly and a connecting rod, defining an offset lever extended between axes of rotation of the eccentric member and a lower end of the connecting rod connected to the crankshaft assembly. The eccentric member is positioned on the crankpin so that the offset lever is perpendicular to the central axis when the piston is in its TDC position. Such an arrangement allows extending a dwell point of a piston and improving connecting rod leverage, thus increasing efficiency of the mechanical conversion process.
The invention is applicable to both two- and four-stroke cycle engines. The invention is also applicable to multi-cylinder engines of various configurations, such as in-line engines, xe2x80x9cVxe2x80x9d engines, and opposed-cylinder engines.